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The aim of this in-vivo study was to exploratively compare the immunologic effect of a CpG-ODN-inhalation combined with specific selected allergens as a local hyposensitisation on COB-affected horses with a CpG-ODN-inhalation alone. The allergen inhalation should be executed in the sense of a local hypo-sensitisation (ASIT), because the COB of the horses has numerous characteristics of a type-I hypersensitivity reaction. The application together with the CpG-ODN as adjuvants has already led to successes in other hypo-sensitisations. But until now it was not tested on COB-diseased horses. In this study it should be investigated whether the combined ASIT-CpG-ODN therapy caused a more marked immunologic effect than the only CpG-ODN-application. Furthermore it should be shown whether the therapy could induce a long term effect after ceasing the inhalation. There were already some studies in which the effect and the tolerance of the CpG-ODN- A 2216 were established on COB-affected horses. In contrast to foreign studies the patients were subjected to inhalation therapy more frequently and were examined again after six weeks to determine a long term effect. In total, 20 moderately COB-affected horses were included in this study. Immediately before the beginning of the study an allergy test (FIT) was carried out on all probands to determine to which allergens the horses reacted sensible. All except three horses reacted positive to several allergens, in particular to mites (dust mite, hay mite, flour mite) and mould antigens. In the FIT some patients reacted even sensitive to the allergens which are found more likely in the summer months, like various pollen of grasses, trees and rape. With a random selection the patients were divided into two groups. Nine horses were only inhaled with the CpG-ODN bound to gelatin nanoparticles as transport medium and eleven horses were, in addition to that, inhaled with two specific selected allergens (dependent on the results of the FIT). The probands were inhaled seven times in an interval of two days. Before the first time of inhalation, two days after the last inhalation and after another six weeks, serum and tracheal wash samples were taken to determine the levels of the different cytokines. By means of ELISA the cytokines IL-4, IL-10, IFN-ү and IL-17 were quantified in the samples. Whereas the IL-17 was quantified only in the tracheal wash samples. For none of the measured cytokines a significant effect of the additionally inhaled allergens could be proven. Therefore the investigated parameters gave no indication that the local hyposensitisation on the immunological level had a better effect on the COB than the mono therapy with CpG-ODN. The IL-4 was significantly regulated down in total. Before the beginning of the study and until six weeks after in the tracheal lavage sample the median decrease of concentration with 14 of 20 horses lay around 49,7 %. In the serum a significant decrease of concentration could only be measured in the last sample after six weeks. This decrease of concentration was also present on 14 of 20 horses, but with a median of 17,4 % relatively low. An upregulation of the Th-1-cytokine IFN-ү and the regulatory IL-10 could not be seen. During the examination period concentrations of both cytokines dropped more or less drastically. The decrease on both cytokines could only be reported after six weeks. A uniform development of the IL-10 expression in the tracheal lavage sample could not be seen. Also on the development of the concentration of the IL-17 no uniform decrease could be seen. There was no correlation with the percentage part of the neutrophil granulocytes in the TBS. The key result of the study is, that an immunological long-term effect over at least six weeks with relatively few inhalations compared to conventional inhalative therapy methods (e.g. cortisone or bronchodilators) without further therapy or change in keeping conditions could be proven by inhalation with the CpG-ODN. During further studies the immunological effect of the CpG-ODN A 2216 inhalation could be tested on in-vitro-isolated BAL-cells of COB-affected horses and on a larger amount of probands to evaluate more measured values statistically. The success of an ASIT on COB-affected horses using inhalation could be proven by itself without CpG-therapy by doing dose response studies at first to evaluate the optimal concentration of the allergen. Also an increase of concentration of the allergen could be considered. Therefore a different way of application would be advised to avoid the risk of an acute bronchospasm. The difficulty to choose the relevant allergens must still be kept in mind. Furthermore a dose response study of the CpG-ODN-inhalation will be an optimal study concept to find out the right concentration of the allergens. In separate studies further research could improve the effectiveness of the interval and the duration of inhalations of the inhalative CpG-ODN application.